WO 2004/113842 A1 discloses a navigation system in which a mobile reception unit, such as a mobile telephone or a PDA, receives position data and forwards the position data to a central control unit arranged in the vehicle, wherein the navigation is performed on the basis of the position data from the mobile reception unit in the central control unit. A drawback of such a two-part navigation system is the high level of technical complexity for the central control unit, which makes the unit expensive, since, apart from the GPS receiver, it comprises all the components which are required for the navigation.